The tutorial only requires 3 layers. The top layer is the picture with the body masked out of the picture.
Step 4 shows the wood layer located below the top layer but the top layer is turned off so you could see what is on the layer. To get to step 5 you just turn on the top layer.
The bottom layer is the reverse mask of the top layer and contains the desaturated metal body pats and has the fill reduced to 90%.
Hopes this helps clarify. Post up your results.